LPM Interference and Cherenkov-like Gluon Bremsstrahlung in Dense Matter

Abstract

Gluon bremsstrahlung induced by multiple parton scattering in a finite dense medium has a unique angular distribution with respect to the initial parton direction. A dead-cone structure with an opening angle ${\theta }_0^2\approx 2(1-z)/(zLE)$ for gluons with fractional energy $z$ arises from the Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's dielectric constant is $ϵ>1$, the LPM interference pattern is shown to become Cherenkov-like with an increased opening angle determined by the dielectric constant ${\cos }^2{\theta }_c=z+(1-z)/ϵ$. For a large dielectric constant $ϵ\gg 1+2/z^{2}LE$, the corresponding total radiative parton energy loss is about twice that from normal gluon bremsstrahlung. Implications of this Cherenkov-like gluon bremsstrahlung to the jet correlation pattern in high-energy heavy-ion collisions is discussed.

Comments: 4 pages in RevTEx with 1 postscript figure